The present invention relates to an epoxy resin-based thermosetting composition affording a cured coated film which is reduced in warp caused by cure shrinkage and is excellent in flexibility, and also to an overcoating material for a flexible circuit board using the same. Further, it relates to a film carrier coated with the overcoating material and to a film device wherein the film carrier is used.
Upon the adhesion between flexible substrates such as packaging materials, films or the like, or upon the coating of these surfaces, it is necessary to reduce as far as possible the influences of cure shrinkage of adhesives or coating materials (i.e., coating agents) to be used therefor or the influences of hardness of the cured products. Therefore, the adhesive or coating agent to be used for such fields of application should necessarily be those which exhibit a small cure shrinkage as far as possible and at the same time, afford cured products having a sufficient flexibility. As thermosetting resin compositions affording flexible cured products, there have hitherto been known compositions comprising, as the main component, a natural or synthetic rubber, urethane-based resin, silicon-based resin, or modified epoxy resin having the skeleton of such rubber or resin. However, such rubber-based resin compositions can be indeed produced relatively at a low cost and the cured products thereof are excellent in flexibility, but they are inferior in weather resistance, heat resistance and chemical resistance. Although it has been attempted to solve these defects, the effects have not been satisfactory. On the contrary, there have been pointed out problems that it is withheld to use chlorinated resins from the viewpoint of the increased understanding of environmental problems, and the like, because such resins sometimes suffer dechlorination upon their use in elevated humidity and temperature environment. Moreover, urethane-based resins also afford cured products excellent in flexibility, but they cannot be said to be satisfactory in weather resistance, chemical resistance, heat resistance, and the like. Furthermore, silicone-based resins whose cured products exhibit both of flexibility and the performances such as weather resistance, chemical resistance, thermal resistance and the like, similarly have defects that the cost of law materials thereof is high and undercoating treatment with a primer is necessary because of their poor adhesiveness to other substrates, and the like. On the other hand, resin compositions comprising, as the main component, an epoxy resin modified with rubber, urethane, or silicon have widely been used because their cured products have an appropriate flexibility and at the same time, performances such as weather resistance, chemical resistance, thermal resistance, and the like. However, any modified epoxy resisin composition has not been yet obtained, whose cured product is sufficiently statisfactory in flexibility and cure shrinkage.
Moreover, with regard to thermosetting resin compositions, as the fields of application thereof which requires electric insulation property, plating resistance and the like, in addition to the above various properties, there may be mentioned surface protecting films for flexible circuit boards whose needs have rapidly increased in recent years. It has been the mainstream to use polyimide films called coverlay films, as the surface protecting films for flexible wiring circuits. The formation of the protecting film using such coverlay film comprises steps of making a die corresponding to the circuit pattern, punching a film for forming the protecting film with the use of the die, and further adhering the punched film onto a substrate with an adhesive. Thus, it is not so preferable in view of the workability because of the complicated steps. On the other hand, a method has been also known, wherein a thermosetting-type overcoating agent as mentioned above, comprising, as the main component, a modified epoxy resin having flexibility or the like, is applied by a screen printing method and then cured. This method is preferable in view of the workability owing to the simple steps, but is still unsatisfactory from the viewpoints of the properties of the cured products such as warp caused by cure shrinkage, flexibility, and the like, so that the method is mainly applied to only the substrates of low added value.
Furthermore, recently, the so-called TAB method using film carriers has been increasingly employed for the purpose of imparting a higher density and a less thickness to an IC package, making use of the technology for forming flexible circuit boards. This method is mainly employed for forming an IC package for driving liquid-crystals. The basic structure of such film carrier is mainly composed of heat-resistant, insulating film base such as polyimide or the like, and an electrical conductor such as copper foil or the like, glued onto the film base through an adhesive containing an epoxy resin as the main component, the wiring pattern having been formed on the copper foil by etching. And, a film carrier device is made by connecting an IC to such tape carrier, followed by sealing with the use of a scaling resin. To prevent the decrease of reliability owing to pattern short, erosion, migration, whisker occurrence, or the like, during the steps before the IC connection, a surface protecting film is usually formed also on such film carrier, using an overcoating agent. As such overcoating agent for film carriers, there have been used an epoxy-based one and a polyimide-based one. However, the former is not satisfactory in warp during curing and flexibility of the coated film, and the latter is not satisfactory in adhesiveness to the IC sealing resin, workability or the like. For these reasons, at present, two or more different overcoating agents are concurrently used to compensate each other (Japanese Patent Application Laid-Open No. 283575/1994).
It is an object of the present invention to provide a thermosetting resin composition which is improved in the occurrence of warp caused by cure shrinkage and the insufficiency in flexibility of the cured products thereof, which are the problems of conventional thermosetting resin compositions. It is another object thereof to provide an epoxy resin-based overcoating agent or material for flexible circuit boards, which has basic properties required of general insulation protective films such as tight adhesiveness, electric insulation property, chemical resistance, thermal resistance, and Sn-plating resistance, and the like. It is still another object of the present invention to provide an overcoating agent which can be used for film carriers for the TAB method. And, it is a further object thereof to provide a film carrier formed by applying the overcoating agent thereonto and a film carrier device using the film carrier.
The present inventors have studied intensively to achieve the above objects, and as the results, found that the concurrent use of not only a single resin having a flexible skeleton as in the prior art, but also a resin whose molecular weight and functional group number per one molecule are restricted to a certain range, as the components of a thermosetting resin composition, results in that the crosslinking density of the cured product thereof can be appropriately regulated, whereby a cured coated film remarkably reduced in warp caused by cure shrinkage and also more excellent in flexibility can be afforded, with the basic properties given by common thermosetting compositions such as tight adhesiveness, electric insulation property, chemical resistance, thermal resistance, and the like being maintained. The present invention has been accomplished on the basis of these findings.
Accordingly, a first thermosetting resin composition of the present invention comprises an epoxy-group(-containing) resin (Component (A)), and a resin (Component (B)) containing a functional group capable of reacting with the epoxy group, such as carboxyl group, amino group, acid anhydride group, hydrazide group, mercapto group, hydroxyl group, isocyanate group or the like and having no blocked carboxyl group, the molecular weight and functional group number per one molecule of both resins being defined as follows. That is, it is a thermosetting resin composition wherein the Component (A) has a number average molecular weight of 800 to 35, 000, an average functional group number of more than 2 per one molecule, and a functional group equivalent of 150 to 2,000 g/mol, and may have a polybutadiene or hydrogenated polybutadiene skeleton, whereas the Component (B) has a number average molecular weight of 800 to 35,000, an average functional group number of more than 2 per one molecule, and a functional group equivalent of 150 to 2,000 g/mol, and contains one or more functional groups selected from amino group, carboxyl group, acid anhydride group, mercapto group, hydroxyl group, isocyanate group and hydrazide group, and contains no blocked carboxyl group, and may have a polybutadiene or hydrogenated polybutadiene skeleton, and the ratio of the Component (B) to the Component (A) is from 0.5 to 2.0 in terms of the overall equivalent number of the functional group(s) of Component (B) capable of reacting with the epoxy group of the Component (A) to the overall equivalent number of the epoxy group of the Component (A).
Furthermore, a second thermosetting resin composition of the present invention is the first thermosetting resin composition wherein other kinds of an epoxy resin (Component (c)) and a resin (Component (d)) are added. That is, it is a thermosetting resin composition wherein an epoxy resin (Component (c)) which has a number average molecular weight of 7,000 to 35,000, an average functional group number of 2 or more per one molecule, and a functional group equivalent of 2,000 to 18,000 g/mol, and which may have a polybutadiene or hydrogenated polybutadiene skeleton is incorporated in combination with the above Component (A), both resins being incorporated in such ratio that the total average equivalent becomes 300 to 2,000 g/mol (both resins being collectively referred to herein as Component (C)), or/and a resin (Component (d)) which has a number average molecular weight of 7,000 to 35,000, an average functional group number of 2 or more per one molecule, and a functional group equivalent of 2, 000 to 18, 000 g/mol, which contains one or more functional groups selected from carboxyl group, amino group, acid anhydride group, hydrazide group, mercapto group, hydroxyl group and isocyanate group, and has no blocked carboxyl group, and which may have a polybutadiene or hydrogenated polybutadiene skeleton is incorporated in combination with the above Component (B), both resins be being incorporated in such ratio that the total average equivalent becomes 300 to 2,000 g/mol (both resins being collectively referred to herein as Component (D)), and the ratio of the Component (D) to the Component (C) is from 0.5 to 2.0 in terms of the overall equivalent number of the functional group(s) of Component (D) capable of reacting with the epoxy group of the Component (C) to the overall equivalent number of the epoxy group of the Component (C).
The present invention also relates to an overcoating agent for flexible circuit boards, wherein the above thermosetting resin composition is employed. The present invention further relates to a film carrier comprising an insulating film and a pattern formed thereon of metal thin film, with a part or all of the insulating film in the folded region having been removed, wherein the circuit pattern side except the joint region including the folded region, is coated with the overcoating agent and cured, and to a film carrier device employing the film carrier.
In the following will be described the present invention in greater detail.
With regard to the properties of cured products resulting from thermosetting resin compositions, thermal resistance, chemical resistance, and the like are properties which are generally improved with the increase of the crosslinking density, while flexibility and the like are properties which are improved with the decrease of the crosslinking density. Moreover, the warp caused by cure shrinkage is reduced with the decrease of the crosslinking density. Therefore, for balancing these properties, the crosslinking density should be properly controlled, and specifically, it is important to use, as components constituting a thermosetting resin composition, those resins which have a certain restricted range of molecular weight and functional group number per one molecule of the resins.
The combined use of the epoxy resin (Component (A)) which has a number average molecular weight of 800 to 35,000, an average functional group number of more than 2 per one molecule, and a functional group equivalent of 150 to 2,000 g/mol, and which may have a polybutadiene or hydrogenated polybutadiene skeleton, and the resin (Component (B)) which has a number average molecular weight of 800 to 35,000, an average functional group number of more than 2 per one molecule, and a functional group equivalent of 150 to 2,000 g/mol, which contains one or more functional groups selected from among carboxyl group, amino group, acid anhydride group, hydrazide group, mercapto group, hydroxyl group and isocyanate group, and has no blocked carboxyl group, and which may have a polybutadiene or hydrogenated polybutadiene skeleton, both resins being used in the thermosetting resin composition of the present invention, is important for imparting well-balancedly both kinds of properties, one being properties such as thermal resistance, chemical resistance and the like which can be achieved at a high crosslinking density, and the other being properties such as flexibility, low shrinkage upon curing, and the like which can be achieved at a low crosslinking density. And, the optimum crosslinking density can be attained by combining Component (A) and Component (B) in a range of 0.5 to 2.0 in terms of equivalent ratio. In particular, when an (epoxy) resin having a double bond such as polybutadiene is to be used, it is more preferable, since the double bonds per as participate slightly in the reaction, to use a resin having a functional group equivalent of about 700 to 2,000 g/mol which is positioned at the upper limit defined according to the present invention or its vicinity with regard to either or both of Components (A) and (B), whereas, when an (epoxy) resin having no double bond such as hydrogenated polybutadiene is to be used, it is more preferable to use a resin having a functional group equivalent of about 300 to 1,300 g/mol with regard to either or both of Components (A) and (B). When the functional group equivalent is smaller than the range, a harder cured product is formed owing to the increased crosslinking density upon curing, whereby a sufficient flexibility cannot be attained for the cured product and also cure shrinkage also becomes large. On the other hand, when the functional group equivalent is larger than the range, more flexible cured product is formed owing to the decreased crosslinking density upon curing, but the cured product is remarkably decreased in thermal resistance and chemical resistance. Moreover, the mixing ratio of Component (A) and Component (B) is out of a range of 0.5 to 2.0, many unreacted functional groups remain even after curing, so that a sufficient curing cannot be achieved, and, in turn, the intended properties cannot be attained.
Since the total functional group equivalent in the system is important for attaining a proper closslinking density, it is also preferable to adjust finely the total equivalent number in the system to its optimum by further incorporating a resin having an equivalent which is out of the above equivalent range. For example, taling up as the epoxy resin, on the one hand, an epoxy resin (Component (c)) which has a number average molecular weight of 7,000 to 35,000, an average functional group number of 2 or more per one molecule, and a functional group equivalent of 2, 000 to 18, 000 g/mol, and which may have a polybutadiene or hydrogenated polybutadiene skeleton, used in combination with the epoxy resin of the above Component (A) (the combination of both resins being collectively herein referred to as Component (C)), both resins being incorporated in such ratio that the total average equivalent becomes 300 to 2,000 g/mol, and on the other hand, a resin (Component (d)) which has a number average molecular weight of 7,000 to 35,000, an average functional group number of 2 or more per one molecule, and a functional group equivalent of 2,000 to 18,000 g/mol, which contains one or more functional groups selected from among carboxyl group, amino group, acid anhydride group, hydrazide group, mercapto group, hydroxyl group and isocyanate group, and has no blocked carboxyl group, and which may have a polybutadiene or hydrogenated polybutadiene skeleton, used in combination with the Component (B) (the combination of both resins being collectively herein referred to as Component (D)), both resins being incorporated in such ratio that the total average equivalent becomes 300 to 2,000 g/mol, then Component (C) and Component (D) can be used as an epoxy resin component corresponding to the above Component (A) and a component having a functional group capable of reacting with the epoxy group corresponding to the above Component (B), respectively. At that time, it is necessary to incorporate the two in such ratio that Component (D) to Component (C) becomes from 0.5 to 2.0 in terms of the overall equivalent number of the functional group(s) of Component (D) capable of reacting with the epoxy group of the Component (C) to the overall equivalent number of the epoxy group of the Component (C).
Component (c) and Component (d) exhibit a function of decreasing the crosslinking density to enhance the flexibility of the cured product and suppress cure shrinkage. Therefore, when their functional group equivalent is less than the range, this effect can not be thoroughly exhibited, and this case is not so preferable. And, when their functional group equivalent is more than the range, sufficient curing cannot be achieved all over the system and the intended physical properties cannot be attained.
Incidentally, the functional group equivalent with regard to carboxyl group, amino group, acid anhydride group, hydrazide group, mercapto group, hydroxyl group and isocyanate group which Component (B) and Component (d) contain, is defined on the basis of the number of reaction points each of which reacts with one epoxy group. For example, since a primary amino group has two active hydrogens capable of reacting with epoxy group, aniline (molecular weight: 93.13), for instance, is counted as bi-functional, and thus, the functional group equivalent thereof is calculated as 46.57.
Moreover, with regard to Components (A), (B), (c), and (d), when a component whose chemical structure has a polybutadiene skeleton is used, a cured resin composition having an increased flexibility can be obtained, and thus this case is preferable. The double bonds in the polybutadiene skeleton are allowed to react gradually, especially under a high temperature air atmosphere, which may, in turn, induce problems such as hardening of coated film and increase of warp, and the like, but these problems can be reduced by hydrogenating 50% or more of the double bonds, and thus this case is further preferable.
Furthermore, with regard to the above Components (A) and (B), the number average molecular weight is preferably 800 to 35,000, more preferably 800 to 25,000. When the molecular weight is larger than this range, the solubility thereof in a solvent decreases and miscibility with another resin having a different structure decreases, so that it becomes difficult to use them as an ingredient of a resin composition. And, even when it is possible to prepare them into a composition, the resulting composition gets increased in stringiness, and thus decreased in applicability onto a substrate. On the other hand, when the molecular weight is smaller than the range, the decrease of flexibility and the large cure shrinkage in the cured product tend to occur, and thus this case is not so preferable. Similarly, with regard to the above Components (c) and (d), the number average molecular weight is preferably 7,000 to 35,000, more preferably 7,000 to 25,000. When the molecular weight is larger than this range, the solubility in a solvent decreases and miscibility with another resin having a different structure decreases, so that it becomes difficult to use them as a component of a resin composition. And, even when it is possible to prepare them into a composition, the large stringiness of the composition is observed and thus the applicability onto a substrate decreases. On the other hand, since Component (c) and Component (d) exhibit a function of enhancing the flexibility of a cured product and inhibiting cure shrinkage, this effect can not be thoroughly exhibited when the molecular weight is smaller than the range, and thus this case is not so preferable.
As a resin containing epoxy group(s) (Component (A)), there maybe mentioned any epoxy resin insofar as it has a number average molecular weight of 800 to 35,000, an average functional group number of more than 2 per one molecule, and a functional group equivalent of 150 to 2,000 g/mol. However, particularly preferred is an epoxy resin having a flexible skeleton. Inter alia, a resin having a polybutadiene skeleton is preferable for imparting a more flexibility, and examples thereof include xe2x80x9cBF1000xe2x80x9d (manufactured by Nippon Soda Co., Ltd.) and the like. More preferred is an epoxy resin having a hydrogenated polybutadiene skeleton, and examples thereof include an epoxydated hydrogenated polybutadiene obtained by partially hydrogenating the double bonds in polybutadiene homopolymer having an average molecular weight of about 1,000 such as xe2x80x9cB-1000xe2x80x9d (manufactured by Nippon Soda Co., Ltd.) or the like, followed by epoxidating the remaining double bonds, an epoxydated hydrogenated polybutadiene obtained by reacting a hydrogenated polybutadiene polyol having an average molecular weight of about 1,000 such as xe2x80x9cGI-1000xe2x80x9d (manufactured by Nippon Soda Co., Ltd.) or the like, with a diisocyanate compound such as 2,4-tolylene diisocyanate or the like, at a ratio of 2 equivalents relative to 1 equivalent of the hydroxyl group of the former polyol in such way that the isocyanate group(s) remain at the terminal(s), followed by adding for addition reaction, to the resulting product, an epoxy compound having one hydroxyl group in one molecule such as xe2x80x9cEpiol G-100xe2x80x9d (manufactured by Nippon Oils and Fats Co., Ltd.), and the like.
As a resin containing epoxy group(s) (Component (c)), there may be mentioned any epoxy resin insofar as it has a number average molecular weight of 7,000 to 35,000, an average functional group number of 2 or more per one molecule, and a functional group equivalent of 2,000 to 18,000 g/mol. However, particularly preferred is an epoxy resin having a flexible skeleton. Inter alia, a resin having a polybutadiene skeleton is preferable for imparting a more flexibility, and examples thereof include an epoxydated hydrogenated polybutadiene obtained by reacting a polybutadiene polyol having an average molecular weight of about 3, 000 such as xe2x80x9cG-3000xe2x80x9d (manufactured by Nippon Soda Co., Ltd.) or the like, with a diisocyanate compound such as 2,4-tolylene diisocyanate or the like, at a ratio of 1 to 2 equivalents relative to 1 equivalent of the hydroxyl group of the former polyol so as to obtain a polymer having a higher molecular weight of about 7,000 to 35,000 in which isocyanate group(s) remain at the terminal(s), followed by adding for addition reaction, to the resulting product, an epoxy compound having one hydroxyl group in one molecule such as xe2x80x9cEpiol G-100xe2x80x9d (manufactured by Nippon oils and Fats Co., Ltd.), and the like. Further, more preferred is a resin having a hydrogenated polybutadiene skeleton, and examples thereof include an epoxydated hydrogenated polybutadiene obtained by reacting a hydrogenated polybutadiene polyol having an average molecular weight of about 3, 000 such as xe2x80x9cGI-3000xe2x80x9d (manufactured by Nippon Soda Co., Ltd.) or the like, with a diisocyanate compound such as 2,4-tolylene diisocyanate or the like, at a ratio of 1 to 2 equivalents relative to 1 equivalent of the hydroxyl group of the former polyol so as to obtain a polymer having a higher molecular weight of about 7,000 to 35,000 in which isocyanate group(s) remain at the terminal(s), followed by adding for addition reaction, to the resulting product, an epoxy compound having one hydroxyl group in one molecule such as xe2x80x9cEpiol G-100xe2x80x9d (manufactured by Nippon Oils and Fats Co., Ltd.), and the like.
As a resin containing one or more functional groups selected from among carboxyl group, amino group, acid anhydride group, hydrazide group, mercapto group, hydroxyl group and isocyanate group and having no blocked carboxyl group (Component (B)), there may be mentioned any resin insofar as it has a number average molecular weight of 800 to 35,000, an average functional group number of more than 2 per one molecule, and a functional group equivalent of 150 to 2,000 g/mol, the said functional group being carboxyl group, amino group, acid anhydride group, hydrazide group, mercapto group, hydroxyl group and/or isocyanate group. However, particularly preferred is a resin having a flexible skeleton. Inter alia, a resin having a polybutadiene skeleton is preferable for imparting a more flexibility, and examples thereof include polybutadienes modified with maleic anhydride such as xe2x80x9cLaicon 130MA13xe2x80x9d and xe2x80x9cLaicon 131MA17xe2x80x9d (both manufactured by Laicon Resin K.K.), and the like, carboxyl-terminated butadiene/acrylonitrile copolymers such as xe2x80x9cHicar CTBN 1300X8xe2x80x9d (manufactured by Ube Industries Ltd.), amine-terminated butadiene/acrylonitril copolymers such as xe2x80x9cHicar CTBN 1300X16xe2x80x9d (manufactured by Ube Industries Ltd.), and the like, polybutadiene polyols such as xe2x80x9cR-45HTxe2x80x9d (manufactured by Idemitsu Petrochemical Co., Ltd.), and xe2x80x9cG-1000xe2x80x9d and xe2x80x9cGQ-1000xe2x80x9d (both manufactured by Nippon Soda Co., Ltd.), and polybutadiene polyisocyanates such as xe2x80x9cHTP-9xe2x80x9d (manufactured by Idemitsu Petrochemical Co., Ltd.), and the like. Furthermore, more preferred are those having a hydrogenated polybutadiene skeleton, and examples thereof include a hydrogenated polybutadiene modified with maleic anhydride obtained by partially hydrogenating double bonds in polybutadiene homopolymer having an average molecular weight of about 1,000 such as xe2x80x9cB-1000xe2x80x9d (manufactured by Nippon Soda Co., Ltd.), followed by modifying the remaining double bonds with maleic anhydride, a hydrogenated polybutadiene polycarboxylic acid obtained by reacting a hydrogenated polybutadiene polyol having an average molecular weight of about 1,000 such as xe2x80x9cGI-1000xe2x80x9d (manufactured by Nippon Soda Co., Ltd.), or the like, with an acid anhydride compound such as trimellitic anhydride in an amount equimolar to 1 equivalent of the hydroxyl group of the former polyol in such way that carboxyl group(s) remain at the terminals), an hydrogenated polybutadiene polyisocyanate obtained by reacting a hydrogenated polybutadiene polyol having an average molecular weight of about 1,000 such as xe2x80x9cGI-1000xe2x80x9d (manufactured by Nippon Soda Co., Ltd.), or the like, with a diisocyanate compound such as 2,4-tolylene diisocyanate at a ratio of 2 equivalents relative to 1 equivalent of the hydroxyl group of the former polyol so that isocyanate group(s) remain at the terminals), and the like.
As a resin containing one or more functional groups selected from among carboxyl group, amino group, acid anhydride group, hydrazide group, mercapto group, hydroxyl group and isocyanate group and having no blocked carboxyl group (Component (d)), there may be mentioned any resin insofar as it has a number average molecular weight of 7,000 to 35,000, an average functional group number of 2 or more per one molecule, and a functional group equivalent of 2,000 to 18,000 g/mol, the said functional group being one or more of carboxyl group, amino group, acid anhydride group, hydrazide group, mercapto group, hydroxyl group and isocyanate group. However, particularly preferred is a resin having a flexible skeleton. Inter alia, a resin having a polybutadiene skeleton is preferable for imparting a more flexibility, and examples thereof include a polybutadiene polycarboxylic acid obtained by reacting a polybutadiene polyol having an average molecular weight of about 3, 000 such as xe2x80x9cG-3000xe2x80x9d (manufactured by Nippon Soda Co., Ltd.), or the like, with a diisocyanate compound such as 2,4-tolylene diisocyanate, or the like, at a ratio of 0.5 to 1 equivalent relative to 1 equivalent of the hydroxyl group of the former polyol so as to obtain a polymer having a higher molecular weight of about 7,000 to 35,000 in which hydroxyl group(s) remain at the terminal(s), followed by reacting the resulting product with an acid anhydride such as trimellitic anhydride or the like, in an amount equimolar to 1 equivalent of the hydroxyl group of the product so that carboxyl group(s) remain at the terminal(s), a polybutadiene polycarboxylic anhydride obtained by reacting a polybutadiene polyol having an average molecular weight of about 3,000 such as xe2x80x9cG-3000xe2x80x9d (manufactured by Nippon Soda Co., Ltd.) or the like, with a diisocyanate compound such as 2,4-tolylene diisocyanate, or the like, at a ratio of 1 to 2 equivalents relative to 1 equivalent of the hydroxyl group of the former polyol so as to obtain a polymer having a higher molecular weight of about 7, 000 to 35,000 in which isocyanate group(s) remain at the terminal(s), followed by reacting the resulting product with a difunctional acid anhydride compound such as benzophenonetetracarboxylic acid dianhydride, or the like, at a ratio of 2 equivalents relative to 1 equivalent of the hydroxyl group so that anhydride group(s) remain at the terminal(s)., and the like. Furthermore, more preferred is a resin having a hydrogenated polybutadiene skeleton, and examples thereof include a hydrogenated polybutadiene polycarboxylic acid obtained by reacting a hydrogenated polybutadiene polyol having an average molecular weight of about 3,000 such as xe2x80x9cGI3000xe2x80x9d (manufactured by Nippon Soda Co., Ltd.), or the like, with a diisocyanate compound such as 2,4-tolylene diisocyanate, or the like, at a ratio of 0.5 to 1 equivalent relative to 1 equivalent of the hydroxyl group of the former polyol so as to obtain a polymer having a higher molecular weight of about 7,000 to 35,000 in which hydroxyl group(s) remain at the terminal (s), followed by reacting the resulting product with an acid anhydride such as trimellitic anhydride or the like, in an amount equimolar to 1 equivalent of the hydroxyl group of the product so that carboxyl group(s) remain at the terminal(s), a hydrogenated polybutadiene polycarboxylic anhydride obtained by reacting xe2x80x9cGI-3000xe2x80x9d with a diisocyanate compound such as 2,4-tolylene diisocyanate, or the like at a ratio of 1 to 2 equivalents relative to 1 equivalent of the hydroxyl group of the former polyol so as to obtain a polymer having a higher molecular weight of about 7,000 to 35,000 in which isocyanate group(s) remain at the terminal(s), followed by reacting the resulting product with a difunctional acid anhydride compound such as benzophenonetetracarboxylic acid dianhydride, or the like, at a ratio of 2 equivalents relative to 1 equivalent of the hydroxyl group so that anhydride group(s) remain at the terminal(s), and the like.
Moreover, the thermosetting resin composition of the present invention may, of course, optionally contain, if required, a curing accelerator for an epoxy resin composition, a filler, an additive, a thixotropic agent, a solvent and the like, in addition to the above essential and desired components. Particularly, in order to further improve bending resistance, fine rubber particles may be preferably added. Moreover, fine polyamide particles may be preferably added to further improve adhesiveness to a base copper circuit, a base material such as a polyimide, polyester film, or the like, and an adhesive layer.
As such fine rubber particles, there may be mentioned any fine particles of a resin exhibiting rubber elasticity such as acrylonitrile butadiene rubber, butadiene rubber, acryl rubber, and the like, which have been subjected to chemical crosslinking treatment to be made insoluble in an organic solvent and infusible. Examples thereof include xe2x80x9cXER-91xe2x80x9d (manufactured by Japan Synthetic Rubber Co., Ltd.), xe2x80x9cStaphyloide AC3355xe2x80x9d, xe2x80x9cStaphyloide AC3832xe2x80x9d and xe2x80x9cIM101xe2x80x9d (manufactured by Takeda Chemical Industries, Ltd.), and xe2x80x9cParaloide EXL2655xe2x80x9d and xe2x80x9cEXL2602xe2x80x9d (manufactured by Kureha Chemical Industries, Co., Ltd.), and the like.
As such fine polyamide particles, there may be mentioned any fine particles of 50 micron or smaller consisting of a resin having an amide linkage, for example, aliphatic polyamides such as nylon, aromatic polyamides such as Kevlar, and polyamidoimides. For example, xe2x80x9cVESTOSINT 2070xe2x80x9d (manufactured by Daicel Huls K.K.) and xe2x80x9cSP500xe2x80x9d (manufactured by Toray Industries, Inc.) may be mentioned.